);
}
};
```
You'd like to test that component without having to manage the
authentication of a user. One option is to mock out that function. This can
be done with some help from [`jest.fn()` and the `mock.mockReturnValue()`
function](https://github.com/jbranchaud/til/blob/master/javascript/mock-a-function-with-return-values-using-jest.md).
```javascript
// MyComponent.test.js
// ... various testing imports
import * as authModules from './authentication';
it('renders the component', () => {
authModules.isAuthenticated = jest.fn().mockReturnValue(true);
const wrapper = shallow();
expect(toJson(wrapper)).toMatchSnapshot();
});
```
By importing the same module and functions used by `MyComponent`, we are
then able to replace them (specifically, `isAuthenticated`) with a mocked
version of the function that returns whatever value we'd like. As
`MyComponent` is being rendered, it will invoked our mocked version of
`isAuthenticated` instead of the actual one.
You could test the other direction like so:
```javascript
authModules.isAuthenticated = jest.fn().mockReturnValue(false);
```
joshbranchaud
April 11, 2018